Cup making machines, such as those manufactured by Paper Machinery Corporation of Milwaukee, Wis., U.S.A. are used to make a variety of cups and containers. A typical cup machine for making paperboard cups, for instance, includes a turret having a plurality of mandrels about which the containers are formed. The turret sequentially rotates the mandrels into cooperation with a variety of workstations where numerous cup forming procedures occur.
In an exemplary procedure, a circular bottom blank is cut at one workstation and attached to the end of a mandrel by a vacuum applied through the mandrel. During this procedure, the outside edge or lip of the bottom blank is folded downwardly. At a subsequent workstation, a sidewall blank is wrapped around the mandrel. The sidewall blank is heated and sealed along a seam which runs generally longitudinally along the side of the cup. (Typically the paperboard is coated with a thermoplastic material, such as polypropylene, so the blanks may be heated and sealed together.)
The sidewall blank extends transversely to the bottom blank except along the lip which runs approximately parallel with the sidewall blank. In some applications, the sidewall blank includes a flap extending beyond the lip of the bottom blank, and this flap is bent over the lip. At a bottom finishing station, the flap is pressed against the lip from an inside recessed area of the bottom of the cup. By heating the polypropylene and firmly pressing the sidewall, sidewall flap, and bottom blank lip together, a seal is formed and the cup is provided with a sturdy bottom region having a recessed area.
There also may be other workstations where various additional cup forming procedures are carried out. For example, one station may be used to provide a curl at the top of the cup to provide a more functional drinking container and a better appearance.
At a typical cup bottom finishing workstation, the bottom of the cup is finished by a knurling wheel which squeezes the bottom blank lip between the lower region of the sidewall and the sidewall flap. The knurling wheel is moved forward first into the recessed area on the bottom side of the cup. Then, the knurling wheel is moved laterally or radially outwardly until it squeezes the sidewall blank, bottom blank lip, and sidewall flap against an abutment wall. Once radially offset, the knurling wheel is rolled about the inside of the arcuate abutment wall until the entire bottom of the cup is pressed together and sealed, typically 11/4 revolutions.
Existing cup bottom finishing workstations have been problematic due to the difficultly of applying sufficient lateral pressure with the knurling wheel to guarantee a strong and lasting seal. Current workstations use either a lever arrangement or a wedge arrangement to drive the knurling wheel to its radially outward position. However with these sliding type mechanisms, application of sufficient pressure to provide desirable sealing characteristics causes rapid wear of the components. Repair or replacement of the components is expensive because the entire cup making machine must be shut down and production halted while the machine is repaired. Thus, it would be advantageous to provide a cup bottom finishing station capable of applying sufficient force in the radial direction without creating excessive wear on the components.